The Familial Factors and Child's Symptomatology Affecting the Age of Diagnosis of Autism Spectrum Disorder

Background:  Genetic and environmental factors have a role in the phenotypic expression of ASD. The signs of ASD usually appear prior to the age of 3 years, but typical symptoms were found as early as 6-12 months of age. Nonetheless, the diagnosis is commonly delayed. The factors that influence the age of diagnosis may be environmental, parental related and symptoms dependant. Early diagnosis and treatment of ASD improves the prognosis.

Objectives: The goal of this research was to identify children’s characteristics that might delay the diagnosis of ASD and to increase the measures of survey in order to make an earlier diagnosis in this population. We focused on the correlation between the age of the diagnosis of ASD and parental experience, in terms of the child’s birth order and whether the child had a former sibling diagnosed with ASD, as well as the parents’ age and education. We also examined the influence of the severity of the autistic disorder’s symptoms on the age of diagnosis.

Methods: The study was conducted at the Autism Center, a national tertiary center for diagnosis, treatment and research in the field of ASD. The cohort included 582 participants, 74 females and 508 males (F:M 1:6.9), aged 15 to 72 months (M=30.9m, SD=12.3m) at the time of diagnosis, all of whom received a diagnosis within the autistic spectrum. Assessment of ASD was obtained using standardized tests, the Autism Diagnosis Interview-Revised (ADI-R) and the Autism Diagnosis Observation Schedule (ADOS) and meeting criteria for autism/ASD based on DSM-IV criteria. Autism severity was assessed by using the new ADOS severity scale. Assessment of adaptive skills was made using the Vineland Adaptive Behavior Scales. Medical, developmental and familial histories were obtained from the parents, including data on child’s gender, age, familial history and parental ages and education. Data was collected between February 2002 and March 2012.

Results: A significantly higher rate of non-first-born children (p<0.05) and a significantly higher rate of children with an older sibling with ASD (p<0.05) was found among children diagnosed earlier with ASD, comparing to the later diagnosed children. Children with developmental regression were diagnosed with ASD significantly earlier than those without regression (p<0.01). The lower the social and communicational functioning level was (by ADOS and ADI), the earlier the diagnosis was made (p<0.001). Lower functioning level in adaptive skills domains (by Vineland) correlated with later diagnosis. No significant correlation was found between the child’s gender, or paternal and/or maternal age or education and the age of diagnosis of ASD.

Conclusions: “Parental experience” (either being non-first-born child or a having an older sibling with ASD), a history of developmental regression and severity of ASD symptoms are all associated with an earlier diagnosis of ASD. Parents should be educated for early signs of ASD to prevent delay in diagnosis. Children who raise any suspicion of clinical signs of ASD should be referred to ASD specialist for extensive evaluation, since milder presentation may also delay the diagnosis.